Table 3.

The distributions of intron locations for housekeeping genes (HKGs) in each genome

Species	Number of HKGs				Ratio of 5′/3′-bias	Extremely 3′-biasedb
	Totala	5′-bias	3′-bias	Equal
C.familiaris	61	29	22	10	1.3	0
G.gallus	55	23	17	15	1.4	0
H.sapiens	86	45	16	25	2.8	0
R.norvegicus	66	35	12	19	2.9	0
P.troglodytes	59	22	20	17	1.1	0
M.musculus	70	34	15	21	2.3	1
A.mellifera	34	15	10	9	1.5	3
C.elegans	48	19	10	19	1.9	5
A.thaliana	38	13	12	13	1.1	2
D.melanogaster	46	24	9	13	2.7	5
A.gambiae	4	2	0	2	–	0
S.pombe	36	16	2	18	8	1
P.falciparum	11	7	0	4	–	0
Y.lipolytica	36	20	0	16	–	0
D.hansenii	34	8	0	26	–	0
E.cuniculi	16	1	0	15	–	0
S.cerevisiae	34	7	0	27	–	0
E.gossypii	33	7	0	26	–	0
K.lactis	35	6	0	29	–	0
C.glabrata	33	6	0	27	–	0
G.theta	8	1	0	7	–	0

^aThe total number of housekeeping genes in each genome except Homo sapiens is chosen using bidirectional best BLASTP hit approach that is explained in detail in the Materials and Methods section.

^bSince our knowledge about the role of genes is still accumulating and evolving, it might be difficult to identify a true set of housekeeping genes for each specific genome.